1. Field of the Invention
The present invention relates to a method for writing servo onto disks of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
FIG. 1 shows a typical track that has a number of fields associated with each sector. A sector may include an automatic gain control (“AGC”) field 1 that is used to adjust the strength of the read signal, a sync field 2 to establish a timing reference for the circuits of the drive, and ID 3 and Gray Code 4 fields to provide sector and track identification.
Each sector may have also a servo field 5 located adjacent to a data field 6. The servo field 5 contains a plurality of servo bits A, B, C and D that are read and used to center the head 7 with the center of the track.
The fields 1–5 must be written onto the disk surfaces during the manufacturing process of the disk drive. These fields are typically written with a servo writer. In one process the fields are written onto a master disk in an off-line servo track writer. The master disk is then assembled into a hard disk drive with a number of blank disks. The assembled drive uses the servo sector written onto the master disk to write another servo sector onto all the disks including the mask disk. The second servo sector is located at a pre-defined time lag from the end of the first servo sector. The off-line servo track writer is capable of writing servo onto all the disks in a copy process.
The conventional servo track writer requires two passes to write servo onto the master disk. The extra pass reduces the efficiency of writing servo and increases the cost of producing the drive. Additionally, only one hard disk drive can be attached to a conventional servo track writer for the servo writing process. This requires a relatively large number of conventional servo track writers which increases the floor space and capital requirements to produce the drives.